To prepare the sponge, place the water in a bowl and add the honey and yeast. Stir. Stir in the white wheat and all-purpose flour until well blended. Cover the bowl with plastic wrap and set aside for 30 minutes.
Mix the grapes with the sugar.
To prepare the bread, stir the olive oil into the sponge, then add the salt. Stir the two flours into the sponge, adding enough additional water until you get a workable dough. Turn the dough out onto the counter and knead until smooth and elastic, about 5 minutes. Oil a large bowl and place the dough into the bowl. Cover and let rise for 45 minutes. Punch down the dough.
Preheat the oven to 400 degrees F. Oil a large baking/cookie sheet and place the dough onto the sheet stretching it with your fingertips to cover the bottom. On one half of the dough scatter half the grapes. Carefully pull the side of the dough not covered with grapes up and over the side that is,  to encase the grapes in dough. Use your fingers to seal the edges together. Scatter the remaining grapes on the top of the flatbread evenly. Bake in the center of the hot oven for about 50 to 55 minutes or until the bread is golden brown and the grapes have softened and split open releasing their juices into the bread. Cool for 10 to 15 minutes before slicing. This bread is delicious warm or at room temperature!